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1.
Abull is the (self-complementary) graph with verticesa, b, c, d, e and edgesab, ac, bc, bd, ce; a graphG is calledBerge if neitherG not its complement contains a chordless cycle whose length is odd and at least five. We prove that bull-free Berge graphs are perfect; a part of our argument relies on a new property of minimal imperfect graphs.This work was done while both authors were at the School of Computer Science, McGill University; support by NSERC is gratefully acknowledged. 相似文献
2.
We study the limiting behavior of the solution of with a Neumann boundary condition or an appropriate Dirichlet condition. The analysis is based on “energy methods”. We assume that the initial data has a “transition layer structure”, i.e., u? ≈ ±+M 1 except near finitely many transition points. We show that, in the limit as ? → 0, the solution maintains its transition layer structure, and the transition points move slower than any power of ?. 相似文献
3.
Summary From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Pb2+(aq)+SrL2+ (nb)↔PbL2+ (nb)+Sr2+ (aq) taking place in the two-phase water-nitrobenzene system (L=PEG 400; aq = aqueous phase, nb = nitrobenzene phase) was
evaluated as logKex(Pb2+, SrL2+)=2.0±0.1. Further, the stability constant of the PEG 400 - lead complex in nitrobenzene saturated with water was calculated
for a temperature of 25 °C: log βnb(PbL2+)=12.9±0.1. 相似文献
4.
E. Makrlík P. Vaňura P. Selucký 《Journal of Radioanalytical and Nuclear Chemistry》2006,267(3):533-535
Summary Extraction of microamounts of calcium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of 18-crown-6 (18C6, L) has been investigated. The equilibrium data have been explained assuming that the
complexes HL+, CaL2+and CaL are extracted into the organic phase. The values of extraction and stability constants of the complex species in nitrobenzene
saturated with water have been determined. 相似文献
5.
It was found that 6-methyl-2-methylthio-4-cyanomethoxypyrimidine (O-isomer) reacted via the cyano group with ammonia and hydroxylamine to give an amldine and an amidoxime respectively. The O-isomer did not react with either primary or secondary amines under similar conditions, but nucleophilic substitution at position 2 of the O-isomer was effected by converting the 2-methylthio group into a 2-methylsu fonyl. 6-Methyl-2methylthio-3-cyanomethylpyrimidinone-4 (N3-isomer) formed imidazo[1, 2-a]pyrirnidinones-5 with ammonia and primary amines, 2-amino-6-methyl-3-cyanomethylpyrirrtidinones-4 with secondary amines and either an amidoxime or an imidazo[1, 2-a]pyrimidinone-5 with hydroxylamine, depending on the reaction temperature.Vilnius University. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 703-707, May, 1996. Original article submitted November 3, 1995. 相似文献
6.
Z. Valentová P. Vaňura E. Makrlík 《Journal of Radioanalytical and Nuclear Chemistry》1997,224(1-2):45-48
Extraction of85Sr by a nitrobenzene solution of bis-1,2-dicarbollylcobaltate in the presence of 15-crown-5 (15C5, L) has been investigated. The equilibrium data and the typical maxima concerning the dependencies of the Sr distribution ratios on the analytical concentration of 15C5 in the system under study can be explained assuming that the HL+, HL2
+ and SrL2
2+ species are extracted into the nitrobenzene phase. The values of the corresponding extraction and stability constants of the extracted species in nitrobenzene saturated with water have been determined. 相似文献
7.
Summary Extraction of microamounts of yttrium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of 15-crown-5 (15C5,L) has been investigated. The equilibrium data have been explained assuming that the
complexes HL+, HL2,+, YL3+, YL2,3+and YH-1L2,2+are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated
with water have been determined. 相似文献
8.
Study on Tonghaosu and Its Analogs: Isolation, Structure Identification and Synthesis of Antifeedant B-ring-homo-tonghaosu 总被引:1,自引:0,他引:1
The methanolic extract from a Chinese endemic Chrysanthemum plant, Dendranthema indicum var. aromaticum, was found to show high antifeeding activity against Pieris brassicae L., and by bioassay-guided separation, the active component, B-ring-homo-tonghaosu, 2-(2‘,4‘-hexadiynylidene)-1,6-dioxaspiro-[4,5]-dec-3-ene (2) was isolated. Its structure was elucidated by comparing its spectroscopic data with those of 2 reported in the literatures. Furthermore new convenient total synthesis methods of B-ring-homo-tonghaosu were also developed to confirm its structure and make its further application in crop protection available. In addition, extensive comparison of spectroscopic data showed that the structure of compound 21 reported in literature should be revised to 2. 相似文献
9.
A. Laurinavi?ius K. Rep?as A. -R. Va?kevi?ius 《International Journal of Infrared and Millimeter Waves》1995,16(7):1217-1222
Power-voltage and frequency characteristics of power heads for 90–120 GHz TE10-mode millimeter waves are presented. Operation of the power heads is based on thermo-e.m.f. of hot charge carriers in silicon. The head has been tested both in the pulsed and continuous generation regime. The experiments were carried out in the power range of 2·10–3–4 W. In the pulse regime, the shortest pulse duration was 1s. 相似文献
10.
Individual extraction constants of some dicarbollylcobaltate anions in the water-nitrobenzene system
E. Makrlík J. Rais K. Baše J. Plešek P. Vaňura 《Journal of Radioanalytical and Nuclear Chemistry》1995,198(2):359-365
Individual extraction constants of nine dicarbollylcobaltate anions in the two-phase water-nitrobenzene system were determined radiometrically assuming that the changes of Gibbs energy of the transfer of the tetraphenylarsonium cation, Ph4As+, and of the tetraphenylborate anion, BPh
4
–
, from the aqueous into the nitrobenzene phase are equal. The constants obtained by this method were correlated with Hansch's constants of hydrophobity. 相似文献